Hydrogels Incorporating GdDOTA: Towards Highly Efficient Dual T(1) /T(2) MRI Contrast Agents

Do not tumble dry: Gadolinium-DOTA encapsulated into polysaccharide nanoparticles (GdDOTA?NPs) exhibited high relaxivity (r(1) =101.7?s(-1) mM(-1) per Gd(3+) ion at 37?°C and 20?MHz). This high relaxation rate is due to efficient Gd loading, reduced tumbling of the Gd complex, and the hydrogel nature of the nanoparticles. The efficacy of the nanoparticles as a T(1) /T(2) dual-mode contrast agent was studied in C6 cells.     

Ab initio study of the solvent H-bonding effect on ESIPT reaction and electronic transitions of 3-hydroxychromone derivatives

The electronic transitions occurring in 4-(N,N-dimethylamino)-3-hydroxyflavone (DMAF) and 2-furanyl-3-hydroxychromone (FHC) were investigated using the TDDFT method in aprotic and protic solvents. The solvent effect was incorporated into the calculations via the PCM formalism. The H-bonding between solute and protic solvent was taken into account by considering a molecular complex between these molecules. To examine the effect of the H-bond on the ESIPT reaction, the absorption and emission wavelengths as well as the energies of the different states that intervene during these electronic transitions were calculated in acetonitrile, ethanol and methanol. The calculated positions of the absorption and emission wavelengths in various solvents were in excellent agreement with the experimental spectra, validating our approach. We found that in DMAF, the hydrogen bonding with protic solvents makes the ESIPT reaction energetically unfavourable, which explains the absence of the ESIPT tautomer emission in protic solvents. In contrast, the excited tautomer state of FHC remains energetically favourable in both aprotic and protic solvents. Comparing our calculations with the previously reported time-resolved fluorescence data, the ESIPT reaction of DMAF in aprotic solvents is reversible because the emitting states are energetically close, whereas in FHC, ESIPT is irreversible because the tautomer state is below the corresponding normal state. Therefore, the ESIPT reaction in DMAF is controlled by the relative energies of the excited states (thermodynamic control), while in FHC the ESIPT is controlled probably by the energetic barrier (kinetic control).     

Single-step versus stepwise two-electron reduction of polyarylpyridiniums: insights from the steric switching of redox potential compression

Contrary to 4,4'-dipyridinium (i.e., archetypal methyl viologen), which is reduced by two single-electron transfers (stepwise reduction), the 4,1'-dipyridinium isomer (so-called "head-to-tail" isomer) undergoes two electron transfers at apparently the same potential (single-step reduction). A combined theoretical and experimental study has been undertaken to establish that the latter electrochemical behavior, also observed for other polyarylpyridinium electrophores, is due to potential compression originating in a large structural rearrangement. Three series of branched expanded pyridiniums (EPs) were prepared: N-aryl-2,4,6-triphenylpyridiniums (Ar-TP), N-aryl-2,3,4,5,6-pentaphenylpyridiniums (Ar-XP), and N-aryl-3,5-dimethyl-2,4,6-triphenylpyridinium (Ar-DMTP). The intramolecular steric strain was tuned via N-pyridinio aryl group (Ar) phenyl (Ph), 4-pyridyl (Py), and 4-pyridylium (qPy) and their bulky 3,5-dimethyl counterparts, xylyl (Xy), lutidyl (Lu), and lutidylium (qLu), respectively. Ferrocenyl subunits as internal redox references were covalently appended to representative electrophores in order to count the electrons involved in EP-centered reduction processes. Depending on the steric constraint around the N-pyridinio site, the two-electron reduction is single-step (Ar = Ph, Py, qPy) or stepwise (Ar = Xy, Lu, qLu). This steric switching of the potential compression is accurately accounted for by ab initio modeling (Density Functional Theory, DFT) that proposes a mechanism for pyramidalization of the N(pyridinio) atom coupled with reduction. When the hybridization change of this atom is hindered (Ar = Xy, Lu, qLu), the first reduction is a one-electron process. Theory also reveals that the single-step two-electron reduction involves couples of redox isomers (electromers) displaying both the axial geometry of native EPs and the pyramidalized geometry of doubly reduced EPs. This picture is confirmed by a combined UV-vis-NIR spectroelectrochemical and time-dependent DFT study: comparison of in situ spectroelectrochemical data with the calculated electronic transitions makes it possible to both evidence the distortion and identify the predicted electromers, which play decisive roles in the electron-transfer mechanism. Last, this mechanism is further supported by in-depth analysis of the electronic structures of electrophores in their various reduction states (including electromeric forms).     

Interplay between Cationic and Neutral Species in the Rhodium‐Catalyzed Hydroaminomethylation Reaction

The reactivity of [Rh(CO)₂{(R,R)‐Ph? BPE}]BF₄ ( 2 ) toward amine, CO and/or H₂ was examined by high‐pressure NMR and IR spectroscopy. The two cationic pentacoordinated species [Rh(CO)₃{(R,R)‐Ph? BPE}]BF₄ ( 4 ) and [Rh(CO)₂(NHC₅H₁₀){(R,R)‐Ph‐BPE}]BF₄ ( 8 ) were identified. The transformation of 2 into the neutral complex [RhH(CO)₂{(R,R)‐Ph? BPE}] ( 3 ) under hydroaminomethylation conditions (CO/H₂, amine) was investigated. The full mechanisms related to the formation of 3 , 4 and 8 starting from 2 are supported by DFT calculations. In particular, the pathway from 2 to 3 revealed the deprotonation by the amine of the dihydride species [Rh(H)₂(CO)₂{(R,R)‐Ph? BPE}]BF₄ ( 6 ), resulting from the oxidative addition of H₂ on 2 .     

Optical manipulation of particle ensembles in air

We demonstrate that airborne light-absorbing particles can be photophoretically trapped and moved inside an optical lattice formed by multiple-beam interference. This technique allows simultaneous three-dimensional manipulation of multiple micro-objects in gases.     

95 GHz millimeter wave signal generation using an arrayed waveguide grating dual wavelength semiconductor laser

We report the generation of a 95?GHz carrier frequency by optical heterodyning of two wavelengths from adjacent channels from an arrayed waveguide grating-based multiwavelength laser. The extended cavity structure of the device provides low phase noise and narrow optical linewidth, further enhanced by the intracavity filter effect of the arrayed waveguide grating. We demonstrate that the generated RF beat note, at 95?GHz, has a -3 dB linewidth of 250?kHz. To the best of our knowledge, this is the narrowest RF linewidth generated from a free-running dual-wavelength semiconductor laser. The device is realized as a photonic integrated circuit using active-passive integration technology, and fabricated on a multiproject wafer run, constituting a novel approach for a compact, low-cost dual-wavelength heterodyne source.     

A phosphine-free Pd catalyst for the selective double carbonylation of aryl iodides

The first phosphine-free Pd-catalysed double carbonylation of aryl iodides is reported as a general and practical method, giving excellent conversions and selectivities for a wide range of aryl iodides and amine nucleophiles under atmospheric CO pressure.     

Lewis acid promoted intramolecular (3 + 2) 'cycloadditions' of methyleneaziridines with alkene and alkyne acceptors

2-Methyleneaziridines can be tethered to a variety of alkene or alkyne acceptors through the saturated carbon of the heterocyclic ring by application of a simple lithiation/alkylation sequence (8 examples, 31-59%). Treatment of the resultant alkene bearing substrates with BF(3)·OEt(2) leads to cis-octahydrocyclopenta[c]pyrroles in which up to four contiguous stereocentres are created in a diastereocontrolled manner after reductive work-up. Using an alkyne based substrate, a 2,4,5,6-tetrahydrocyclopenta[c]pyrrole is produced by rapid tautomerisation of the initially formed bisenamine. Evidence that these (3 + 2) 'cycloadditions' proceed in a stepwise manner via a 2-aminoallyl cation is presented.